CN111010684A - Internet of vehicles resource allocation method based on MEC cache service - Google Patents

Internet of vehicles resource allocation method based on MEC cache service Download PDF

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CN111010684A
CN111010684A CN201911298296.9A CN201911298296A CN111010684A CN 111010684 A CN111010684 A CN 111010684A CN 201911298296 A CN201911298296 A CN 201911298296A CN 111010684 A CN111010684 A CN 111010684A
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vehicle
task
time delay
internet
vehicles
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CN111010684B (en
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张海波
张益峰
许云飞
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Chongqing University of Post and Telecommunications
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/30—Services specially adapted for particular environments, situations or purposes
    • H04W4/40—Services specially adapted for particular environments, situations or purposes for vehicles, e.g. vehicle-to-pedestrians [V2P]
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W4/00—Services specially adapted for wireless communication networks; Facilities therefor
    • H04W4/80—Services using short range communication, e.g. near-field communication [NFC], radio-frequency identification [RFID] or low energy communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W72/00—Local resource management
    • H04W72/50—Allocation or scheduling criteria for wireless resources
    • H04W72/53—Allocation or scheduling criteria for wireless resources based on regulatory allocation policies
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/40—Engine management systems

Abstract

The invention relates to the technical field of wireless short-distance communication of Internet of vehicles, in particular to an Internet of vehicles resource allocation method based on MEC cache service; the method comprises the following steps: determining a time delay function of a vehicle user according to an optimization target of the internet of vehicles resource allocation; the method comprises the steps of solving a time delay function optimal value of a vehicle user through an improved generalized benders decomposition method, and performing vehicle networking resource allocation by adopting server communication resources, server computing resources and server cache resources when the time delay function optimal value is adopted; the invention simultaneously determines the resource allocation method of the Internet of vehicles from three aspects of calculation unloading, resource allocation and content caching, and reduces time complexity, total time delay of users and better experience for the users by the improved generalized benders decomposition method.

Description

Internet of vehicles resource allocation method based on MEC cache service
Technical Field
The invention relates to the technical field of wireless short-distance communication of Internet of vehicles, in particular to an Internet of vehicles resource allocation method based on MEC cache service.
Background
The internet of vehicles has gained wide attention and research at home and abroad as the most potential development and application of the internet of things theory in the intelligent traffic system. The concept of the car networking is developed through a mobile ad hoc network and a vehicle-mounted sensor network, and finally, the concept of the communication between the car and the X is developed. The traditional applications of the internet of vehicles are mainly safety applications, aiming to relieve and reduce congestion and accidents in the traditional traffic field, thereby assisting traffic management. However, with the continuous abundance of the vehicle traveling demands of people, the application of the car networking entertainment information service class also gets more attention. The transmission of entertainment information in the internet of vehicles has two important characteristics: (1) the data volume is relatively large, the bandwidth resource occupied by content acquisition is large, and the transmission time is long. (2) Data is popular content and is requested by a vehicle a large number of times. Mobile Edge Computing (MEC) is a new technology featuring high bandwidth and low latency that can provide service environment and computing power at the edge of various other mobile networks, reducing network operation and service delivery latency by moving vehicles closer. The technology with very strict delay requirement, namely the internet of vehicles, is just one of the typical application scenarios of the MEC.
The MEC can cause the mobile devices to send their computing tasks to the MEC server via wireless transmission to perform task offloading. Each vehicle is then associated with a clone in the MEC server, which performs the computing task in place of the vehicle. Many previous efforts have been delved into computing offload issues in terms of latency reduction, power savings, and quality of service, respectively. In addition, the server in the MEC system may implement an in-network caching function, which can reduce duplicate information transmissions, similar to the function provided by an information-centric network (ICN). Currently, there is much research effort devoted to caching strategies. For example, the problem of memory allocation in the cache of the base station is studied and analyzed by optimizing a cache scheme by minimizing the number of requests for macro base station services. Still other efforts have been directed to maximizing overall system revenue, e.g., saving radio resources, computing resources, and backhaul bandwidth. The proposed solution is not efficient when specific optimal goals are involved, such as total latency or energy consumption. Some have created a joint problem of buffering, computation and bandwidth resource allocation in order to minimize the combined cost of network usage and energy consumption, but communication resource allocation is not considered.
The current research is dedicated to research on unilateral or bilateral calculation unloading, resource allocation and content caching, but the three aspects are rarely considered together in the prior work, so that when the vehicle networking resource allocation is carried out, the allocation of calculation resources, caching resources and communication resources is unreasonable, the local resource allocation is better, the overall resource allocation is unreasonable, and the user service experience is poor.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a vehicle networking resource allocation method based on MEC cache service, which comprises the following steps:
determining a time delay function of a vehicle user according to an optimization target of the internet of vehicles resource allocation; and (3) solving a time delay function optimal value of the vehicle user through an improved generalized benders decomposition method, and performing vehicle networking resource allocation by adopting server communication resources, server computing resources and server cache resources when the time delay function optimal value is adopted.
Preferably, the optimization objective of the vehicle networking resource allocation comprises: vehicle task local computation delay function
Figure BDA0002321177560000021
Vehicle task edge calculation delay function
Figure BDA0002321177560000022
Vehicle mission uplink transmission delay function
Figure BDA0002321177560000023
Server cached latency function
Figure BDA0002321177560000024
Preferably, the expression of the vehicle task local computation delay function is as follows:
Figure BDA0002321177560000025
preferably, the calculation process of the vehicle task edge calculation delay function includes: the MEC server on the macro base station can provide calculation unloading service for a plurality of vehicles at the same time, and the vehicles receive the unloading taskAfter the service, the server replaces the vehicle to execute the task, and the expression of the vehicle task edge calculation time delay function is as follows:
Figure BDA0002321177560000026
preferably, the expression of the vehicle task uplink transmission delay function is as follows:
Figure BDA0002321177560000027
preferably, the expression of the server cached delay function is as follows:
Figure BDA0002321177560000028
further, the determining a time delay function of the vehicle user according to the optimization goal of the internet of vehicles resource allocation includes: weighting the optimization target of the vehicle networking resource allocation to obtain a time delay function of the vehicle user, wherein the expression is as follows:
Figure BDA0002321177560000031
preferably, the obtaining of the optimal value of the time delay function of the vehicle user through the improved generalized benders decomposition method includes: the method adopts a generalized Becders decomposition method to decompose the time delay function of the vehicle user into a main problem and a sub problem, and comprises the following steps:
step 1: according to the generalized Becders decomposition method, a sub-problem is obtained by fixing the unloading decision and the caching decision binary vector in the time delay function of the vehicle user; and the subproblems have optimal solutions;
step 2: if the subproblem can be solved, the subproblem has a unique continuous solution, and the corresponding Lagrange multiplier lambda is obtained, and the optimal objective function value of the subproblem is the effective upper bound of the time delay function of the vehicle user; obtaining a feasible cut of the sub-problem according to the continuous solution, and adding the feasible cut into the main problem as a constraint condition;
if the subproblem does not have a feasible solution, zooming the subproblem to obtain the subproblem with the feasible solution; solving the subproblems with feasible solutions by using a Lagrange method, simultaneously solving the infeasible segmentations of the subproblems by using an external approximation method, and adding the infeasible segmentations into the main problem as constraint conditions;
and step 3: solving a main problem min of a time delay function of a vehicle user according to constraint conditions of feasible cutting and infeasible cuttingeG; performing finite iteration on the main problem according to constraint conditions of feasible cutting and infeasible cutting and constraint conditions of integer cutting to obtain an optimal objective function value of the main problem, wherein the function value is an effective lower bound of a delay function of a vehicle user;
and 4, step 4: checking each unloading decision and caching decision according to a time delay function of a vehicle user;
and 5: the unloading task is converted into a vehicle local calculation task, so that the total time delay of a vehicle user is reduced;
step 6: stopping the check when the total time delay of the vehicle user reaches the minimum value; and simultaneously outputting the unloading decision, the caching decision and the resource allocation strategy at the moment, wherein the strategies are the optimal resource allocation scheme.
The invention simultaneously determines the resource allocation method of the Internet of vehicles from three aspects of calculation unloading, resource allocation and content caching, thereby realizing the optimal allocation mode of the resources of the Internet of vehicles; according to the invention, through the improved generalized benders decomposition method, the time complexity is reduced, the total time delay of the user is reduced, and better experience is provided for the user.
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FIG. 1 is a schematic diagram of a resource allocation architecture model based on MEC cache service in the Internet of vehicles according to the present invention;
FIG. 2 is a flowchart of an embodiment of resource allocation based on MEC cache service in the Internet of vehicles according to the present invention;
FIG. 3 is a flow chart of the improved generalized benders decomposition method for reducing algorithm time complexity according to the present invention;
FIG. 4 is a graph comparing the effect of system bandwidth on total delay in accordance with the present invention with other methods;
fig. 5 is a graph comparing the effect of the present invention on the computing power of the MEC server versus other methods on the total latency.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the technical solutions in the embodiments of the present invention are described below clearly and completely with reference to the data and the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments.
As shown in FIG. 1, during the driving process of the vehicle, the user has service requirements, and calculation tasks are generated. Because the vehicle has limited computing capacity, the vehicle can send the task to a nearby base station, an MEC server equipped in the base station can assist in computing the task, and if the base station caches partial content, repeated information transmission can be reduced, so that computing time can be reduced. The intermediate process involves resource allocation of communication resources, computing resources and cache resources. In order to reasonably quantify these resources for optimization, model building is performed.
A method for allocating resources of a vehicle networking based on MEC cache service is shown in FIG. 2 and comprises the following steps: determining a time delay function of a vehicle user according to an optimization target of the internet of vehicles resource allocation; the method comprises the steps of solving a time delay function optimal value of a vehicle user through an improved generalized benders decomposition method, and performing vehicle networking resource allocation by adopting server communication resources, server computing resources and server cache resources when the time delay function optimal value is adopted; where MEC represents moving edge computation and benders represents mixed integer programming algorithm.
The optimization objective of the vehicle networking resource allocation comprises the following steps: vehicle task local computation delay function
Figure BDA0002321177560000041
Vehicle task edge calculation delay function
Figure BDA0002321177560000042
Vehicle mission uplink transmission delay function
Figure BDA0002321177560000043
Server cached latency function
Figure BDA0002321177560000044
The processing procedure of the car networking system comprises the following steps:
the vehicle heterogeneous network comprises a vehicle heterogeneous network with multiple vehicles and a macro base station, wherein an MEC server is deployed on one side of the macro base station; the MEC server comprises a computing and storing resource function; the computing resources are connected to the Internet through the core network of the cellular communication system, thereby providing task processing; the storage resource provides task content and codes and determines whether to store the content;
if the content is stored, the content can be reused;
associating the vehicles with the macro base station by orthogonal frequency division multiplexing if the content is not stored, wherein the spectrum resources allocated to each vehicle cannot be reused;
the vehicles follow the poisson distribution, and the vehicle set is defined as
Figure BDA0002321177560000051
Each vehicle v in the set has a computing task at a time, denoted as
Figure BDA0002321177560000052
For task offloading, define xvE {0, 1} is the unload decision for vehicle v, xv1 denotes vehicle v selects offload to MEC server execution, xv0 means that vehicle v chooses to compute locally;
for task caching, definition αvC {0, 1} is the cache decision for vehicle v, αv1 indicates that the MEC server chooses to cache the content requested by vehicle v, αv0 means that the MEC server does not select to cache the content requested by the vehicle v;
where N denotes the largest number in the set of vehicles, svIndicating the size of the input data, cvRepresenting the workload, i.e. the amount of computation to complete a task,
Figure BDA0002321177560000053
indicating the maximum tolerance latency.
Vehicle mission uplink transmission delay function
Figure BDA0002321177560000054
The calculation process of (2) includes:
vehicle selection offloads computing tasks to the MEC server; sending the input data of the task to the MEC server; calculating the uplink transmission spectrum efficiency of the vehicle as follows:
Figure BDA0002321177560000055
the available bandwidth of the whole system is B, and the whole bandwidth is divided into each vehicle by a ratio; percentage of bandwidth is dvE (0, 1), the uplink transmission rate of the vehicle is:
Figure BDA0002321177560000056
the vehicle selects to carry out unloading calculation on the task, accesses to a corresponding macro base station through wireless transmission, and then loads the task to an MEC server for calculation; for a vehicle with an unloaded task, corresponding transmission time delay is generated when the vehicle is transmitted to the MEC, and according to a communication model, the uplink transmission time delay of the vehicle is as follows:
Figure BDA0002321177560000057
wherein r isvRepresenting the uplink transmission spectral efficiency, p, of the vehiclevRepresenting the transmission power of the vehicle, hvRepresenting the channel gain, σ, of the vehicle and the macro base station2Which is indicative of the power of the noise,
Figure BDA0002321177560000061
representing the upstream transmission rate of the vehicle, dvRepresenting the vehicle's upstream transmission rate, B representing the system bandwidth,
Figure BDA0002321177560000062
representing the uplink transmission delay, tra representing the uplink transmission, SvAnd represents the calculation task input data size.
The server computing process comprises the following steps: the method comprises the steps that a vehicle task local calculation time delay function and a vehicle task edge calculation time delay function are obtained;
the local computation includes: the vehicle carries out calculation by itself, and the calculation result is
Figure BDA0002321177560000063
And is
Figure BDA0002321177560000064
Vehicle user performing local task TvThe time of execution of the calculation is:
Figure BDA0002321177560000065
wherein the content of the first and second substances,
Figure BDA0002321177560000066
representing the computing power of the vehicle itself, cvThe workload is represented by a representation of the workload,
Figure BDA0002321177560000067
representing the local computation time delay;
the edge calculation includes: the MEC server on each macro base station can provide calculation unloading service for a plurality of vehicles at the same time, and the maximum calculation resource shared by each MEC server to the associated vehicles is fmax(ii) a After the vehicle receives the unloading task, the server replaces the vehicle to execute the task, and the percentage of computing resources distributed to the vehicle v by the MEC server is qvE (0, 1), the edge computed delay is:
Figure BDA0002321177560000068
wherein the content of the first and second substances,
Figure BDA0002321177560000069
representing edge computation time delay, fmaxRepresenting maximum calculation provided by MEC server to associated vehicle sharesAnd (4) resources.
Server cached latency function
Figure BDA00023211775600000610
The calculation process of (2) includes:
determining the maximum cache of the MEC server as Ce(ii) a The task is unloaded to the MEC server, the server can request the content from the Internet, the popularity of the requested content follows Zipf distribution, and the popularity of the vehicle v for requesting the task k is as follows:
Figure BDA00023211775600000611
wherein N isfRepresents the overall type of content in Intemet, τ represents the Zipf distribution parameter, Zipf distribution is a power law distribution, k represents the requested task, pv(k) Represents the popularity of the vehicle v to request the task k;
if the requested content is cached, the backhaul time and backhaul bandwidth between the macro base station and the Internet can be obtained; when the average transmission rate of Internet data is Q, the return bandwidth of the vehicle v for requesting the task k is as follows:
Figure BDA0002321177560000071
when the size of the task content request is K, the return delay is
Figure BDA0002321177560000072
Wherein the content of the first and second substances,
Figure BDA0002321177560000073
indicating that vehicle v requests city-back bandwidth for task k,
Figure BDA0002321177560000074
indicating a time delay back to town.
The user service total delay model is used for calculating the total delay of unloading the tasks to the MEC server by the vehicle v, and the expression is as follows:
Figure BDA0002321177560000075
wherein the content of the first and second substances,
Figure BDA0002321177560000076
which represents the total time delay and is,
Figure BDA0002321177560000077
which indicates the time delay of the uplink transmission,
Figure BDA0002321177560000078
indicating edge computation time delay, αvThe decision to cache is represented by a cache table,
Figure BDA0002321177560000079
indicating the backhaul delay.
Since the tasks are calculated locally and marginally, the total task duration for a single vehicle can be expressed as
Figure BDA00023211775600000710
The total time delay of the whole system is reduced while the service quality is ensured. By deploying task caching, offloading, and resource allocation strategies to minimize overall system latency for vehicle users. Weighting the optimization target of the vehicle networking resource allocation to obtain a time delay function of the vehicle user, wherein the expression is as follows:
Figure BDA00023211775600000711
wherein the limiting conditions include: c1:
Figure BDA00023211775600000712
C2：
Figure BDA00023211775600000713
C3：
Figure BDA00023211775600000714
Figure BDA00023211775600000715
C4：
Figure BDA00023211775600000716
C5：
Figure BDA00023211775600000717
C6：
Figure BDA00023211775600000718
C7：
Figure BDA00023211775600000719
Figure BDA00023211775600000720
C8：
Figure BDA00023211775600000721
and C9:
Figure BDA00023211775600000722
c1 and C2 represent binary variables in unloading decision and caching decision respectively, C3 represents that vehicles with unloading tasks make spectrum decision, C4 represents that the sum of spectrum resources allocated to the vehicles with unloading tasks cannot exceed the total spectrum bandwidth, C5 represents that vehicles with unloading tasks make computing resource decision, C6 represents that the sum of computing resources allocated to the unloading tasks cannot exceed the total computing capacity of the MEC server, C7 represents that the vehicles with unloading tasks need to request content from the Internet, C8 represents that the sum of content cached from the Internet cannot exceed the storage capacity of the MEC server, and C9 represents that the total delay of each vehicle computing task should meet the maximum tolerance delay;
wherein x isvRepresents an offload decision, svRepresenting the size of the input data of the computing task, dvRepresenting the percentage of the frequency bandwidth, B representing the system bandwidth, rvRepresenting the uplink transmission spectral efficiency of the vehicle, cvRepresenting the workload, qvRepresenting the percentage of computing resources, f, assigned by the MEC server to the vehicle vmaxRepresenting the maximum computing resources that the MEC server provides for the associated vehicle to share, αvRepresenting a caching decision, K representing a task content request size, tau representing a Zipf distribution parameter, K representing a requested task, NfIndicating the overall type of content in the Internet, Q the average transmission rate of the Intemet data,
Figure BDA0002321177560000081
which represents the own computing power of the vehicle,
Figure BDA0002321177560000082
which represents the total time delay and is,
Figure BDA0002321177560000083
which represents the time delay calculated locally,
Figure BDA0002321177560000084
indicating the maximum tolerance latency.
As shown in fig. 3, in order to reduce the computational complexity of the user service delay function, a generalized Becders decomposition method is introduced. The generalized Becders decomposition method decomposes an integer vector and a continuous vector into a main problem and a sub problem, respectively. The main problem is the mixed integer linear programming problem and the sub-problem is the non-linear programming problem. The optimal solution to the original problem can be obtained by iteratively solving the main problem and the sub-problems.
Step 1: according to the generalized Becders decomposition method, the sub-problem is obtained by fixing the unloading decision and the caching decision binary vectors in the original optimization problem.
Figure BDA0002321177560000085
Wherein the limiting conditions include: c3:
Figure BDA0002321177560000086
C4：
Figure BDA0002321177560000087
C5：
Figure BDA0002321177560000088
Figure BDA0002321177560000089
C6：
Figure BDA00023211775600000810
C7：
Figure BDA00023211775600000811
C8：
Figure BDA00023211775600000812
and C9:
Figure BDA00023211775600000813
by fixing the binary vectors of the unload decision x and the cache decision α, it is determined that the sub-problem has the best solution.
Step 2: if the subproblem can be solved, the subproblem has a unique continuous solution, and the corresponding Lagrange multiplier lambda is solved, and the optimal objective function value of the subproblem is the effective upper bound of the original problem; obtaining a feasible cut of the sub-problem according to the continuous solution, and adding the feasible cut into the main problem as a constraint condition;
defining H (x, α, d, q) as a sub-problem constraint set, wherein
Figure BDA0002321177560000091
At this point, the sub-problem may be converted to:
Figure BDA0002321177560000092
H(x*，α*，d，q)≤0
order to
Figure BDA0002321177560000093
When the sub-problem has a feasible solution, we can get a feasible cut and add it as a constraint to the main problem, for convenience of representation, the sets (x, α) and (d, q) are represented by e and o, respectively.
Figure BDA0002321177560000094
The subproblems do not have feasible solutions, and the subproblems are scaled to obtain the subproblems with feasible solutions; solving the subproblems with feasible solutions by using a Lagrange method, simultaneously solving the infeasible segmentations of the subproblems by using an external approximation method, and adding the infeasible segmentations into the main problem as constraint conditions;
Figure BDA0002321177560000095
Figure BDA0002321177560000096
wherein η denotes the relaxation vector, η and H (o, e)*) The lengths of the two sub-problems are all 4N +3, in this case, the sub-problem without a feasible solution is changed into the sub-problem with a feasible solution, the Lagrangian method is also used for solving the optimal objective function value, the corresponding Lagrangian multiplier is restrained to be gamma, in order to accelerate the convergence of the relaxation sub-problem and reduce the complexity of the calculation time of the optimization problem, the infeasible cutting of the problem is solved by adopting an outer approximation method:
Figure BDA0002321177560000101
wherein, FifA functional expression representing the lagrange method,
Figure BDA0002321177560000102
the gradient transformation sign of the lagrange decomposition method is shown.
And step 3: from feasible cut and infeasible cut determinationsThe main problem of solving the binary variable is mineG；
Ff(e)-G≤0
Fif(e，o)≤0
Figure BDA0002321177560000103
The first two constraints of the main problem are the satisfied conditions of all feasible segmentations and infeasible segmentations, and the third constraint is an integer segmentation to exclude infeasible binary vectors. In the third constraint, the first constraint is that,
Figure BDA0002321177560000104
wherein ej∈{0，1}，
Figure BDA0002321177560000105
And (4) carrying out finite iteration on the main problem and the sub-problems of the original problem to obtain the optimal objective function value of the time delay function of the vehicle user, wherein the optimal objective function value is also the effective lower bound of the original problem.
And 4, step 4: checking each unloading decision and caching decision according to a time delay function of a vehicle user;
and 5: the unloading task is converted into a vehicle local calculation task, so that the total time delay of a vehicle user is reduced;
step 6: stopping the check when the total time delay of the vehicle user reaches the minimum value; and simultaneously outputting the unloading decision, the caching decision and the resource allocation strategy at the moment, wherein the strategies are the optimal resource allocation scheme.
Based on the generalized benders decomposition algorithm, we provide a resource allocation scheme based on MEC cache service in the Internet of vehicles, such as algorithm 1
Figure BDA0002321177560000106
Figure BDA0002321177560000111
Figure BDA0002321177560000112
Figure BDA0002321177560000121
Algorithm 1 consists essentially of two parts, namely: and (6) decision making and checking. The method solves the subproblems with feasible solutions and the new subproblems without feasible solutions by fixing binary variables, then solves the main problem under the condition that all feasible segmentations and infeasible segmentations meet, and terminates in finite iterations. Checking each offload decision and cache decision according to the original optimization problem; if the total delay can be reduced by deleting the unloading task, the corresponding task is converted into local execution; the checking operation terminates until the total delay ceases to decrease; after the checking operation is completed, the optimal offloading, caching decision and resource allocation strategy can be determined at the same time.
As shown in fig. 4, as the number of vehicles increases, the total time delay of the system increases. When all tasks of the vehicle are performed locally, the total system latency is always higher than the solution proposed herein. The reason is that the computing power of the vehicle is limited and the MEC server computing power is not fully utilized. The total time delay for the vehicle to select full off-load increases significantly as the number of vehicles increases, even beyond all local wait time expenditures. The reason is that communication and computing resources are limited and less resources are allocated to each offload task, resulting in a significant increase in the overall system latency. The difference between the total system delay between the scheme and the exhaustion method is small and is within 0.2s, and the difference between the waiting time of the heuristic algorithm and the total system delay is within 0.3 s.
As shown in fig. 5, the method of the present invention is compared with other methods in terms of system bandwidth and simulation of the effect on the total delay of the whole system. In the invention, the allocation of frequency spectrum and computing resources is comprehensively considered. In order to study the influence of resource allocation on the delay performance, on the premise that the number of vehicles is 10, the total system delay is reduced along with the increase of the system bandwidth, and the time gap between the four schemes generally has a reduced trend, because more spectrum resources increase the transmission rate of the vehicles, thereby reducing the total system delay. In addition, the total system time delay of the equal spectrum resources is more than that of the other three schemes, because of numerous tasks at the bottom layer, the equal spectrum resource allocation cannot provide more resources for large-scale computing tasks, but provides too many resources for small-scale computing tasks, thereby causing extra delay and resource waste, and further proving the superiority of the scheme.
The above-mentioned embodiments, which further illustrate the objects, technical solutions and advantages of the present invention, should be understood that the above-mentioned embodiments are only preferred embodiments of the present invention, and should not be construed as limiting the present invention, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (8)

1. A vehicle networking resource allocation method based on MEC cache service is characterized in that: determining a time delay function of a vehicle user according to an optimization target of the internet of vehicles resource allocation; the method comprises the steps of solving a time delay function optimal value of a vehicle user through an improved generalized benders decomposition method, and performing vehicle networking resource allocation by adopting server communication resources, server computing resources and server cache resources when the time delay function optimal value is adopted; where MEC represents moving edge computation and benders represents mixed integer programming algorithm.
2. The method for allocating resources in the internet of vehicles based on the MEC cache service as claimed in claim 1, wherein: the optimization objective of the vehicle networking resource allocation comprises the following steps: vehicle task local computation delay function
Figure FDA0002321177550000011
Vehicle task edge calculation delay function
Figure FDA0002321177550000012
Vehicle mission uplink transmission delay function
Figure FDA0002321177550000013
Server cached latency function
Figure FDA0002321177550000014
3. The method for allocating resources in the internet of vehicles based on MEC cache service of claim 2, wherein the vehicle task locally calculates the time delay function
Figure FDA0002321177550000015
The expression of (a) is:
Figure FDA0002321177550000016
wherein the content of the first and second substances,
Figure FDA0002321177550000017
representing the computing power of the vehicle itself, cvRepresenting the workload.
4. The method for allocating resources of the internet of vehicles based on the MEC cache service as claimed in claim 2, wherein the vehicle task edge calculates a time delay function
Figure FDA0002321177550000018
The calculation process of (2) includes: the MEC server on the macro base station can provide calculation unloading services for a plurality of vehicles at the same time, after the vehicles receive unloading tasks, the server replaces the vehicles to execute the tasks, and the expression of the calculation delay function of the vehicle task edge is as follows:
Figure FDA0002321177550000019
wherein f ismaxRepresenting the maximum computing resource that the MEC server provides for the associated vehicle to share, qvRepresents the percentage of computing resources assigned to vehicle v by the MEC server, and qv∈(0，1)。
5. The method for allocating resources of the internet of vehicles based on the MEC cache service as claimed in claim 2, wherein the vehicle task uplink transmission delay function
Figure FDA00023211775500000110
The calculation process of (2) includes:
step 1: vehicle selection offloads computing tasks to the MEC server;
step 2: sending the input data of the task to the MEC server, and calculating the uplink transmission spectrum efficiency r of the vehiclev；
And step 3: determining the bandwidth B of the Internet of vehicles, dividing the bandwidth into each vehicle in the Internet of vehicles to obtain the bandwidth percentage d of the vehiclesvAnd calculating the uplink transmission rate of the vehicle by combining the uplink transmission spectrum efficiency
Figure FDA0002321177550000021
And 4, step 4: when a vehicle for calculating task unloading transmits a task to the MEC, corresponding transmission time delay is generated, and the uplink transmission time delay of the vehicle is as follows:
Figure FDA0002321177550000022
wherein r isvRepresenting the uplink transmission spectral efficiency of the vehicle, B representing the vehicle networking bandwidth, SvRepresenting the computing task input data size.
6. The method for allocating resources in the internet of vehicles based on MEC cache service as claimed in claim 2, wherein the delay function of the server cache
Figure FDA0002321177550000023
The calculation process of (2) includes:
step 1: determining the maximum cache of the MEC server as Ce；
Step 2: unloading the vehicle unloading task to an MEC server, requesting content from the Internet by the server, requesting the size K of the task content, following Zipf distribution, calculating the popularity p of the vehicle v requesting the task Kv(k)；
And step 3: the requested content is cached, and the backhaul bandwidth of the vehicle v for the task k is acquired
Figure FDA0002321177550000024
And 4, step 4: calculating a server cache latency function as
Figure FDA0002321177550000025
Wherein K represents the size of the task content request, Zipf distribution is power law distribution,
Figure FDA0002321177550000026
indicating that vehicle v requests the backhaul bandwidth for task k.
7. The method for allocating resources in the internet of vehicles based on the MEC cache service as claimed in claim 1, wherein: the determining of the time delay function of the vehicle user according to the optimization objective of the internet of vehicles resource allocation comprises the following steps: weighting the optimization target of the vehicle networking resource allocation to obtain a time delay function of the vehicle user, wherein the expression is as follows:
Figure FDA0002321177550000031
wherein x isvRepresents an offload decision, svRepresenting the size of the input data of the computing task, dvRepresenting the percentage of the frequency bandwidth, B representing the system bandwidth, rvRepresenting the uplink transmission spectral efficiency of the vehicle, cvRepresenting the workload, qvRepresenting computational resources allocated by MEC server to vehicle vPercentage of source, fmaxRepresenting the maximum computing resources that the MEC server provides for the associated vehicle to share, αvRepresenting a caching decision, K representing a task content request size, tau representing a Zipf distribution parameter, K representing a requested task, NfIndicating the overall type of content in the Internet, Q the average transmission rate of Internet data,
Figure FDA0002321177550000032
which represents the own computing power of the vehicle,
Figure FDA0002321177550000033
which represents the total time delay and is,
Figure FDA0002321177550000034
which represents the time delay calculated locally,
Figure FDA0002321177550000035
indicating the maximum tolerance latency.
8. The method for allocating resources in the internet of vehicles based on the MEC cache service as claimed in claim 1, wherein: the method for solving the time delay function optimal value of the vehicle user through the improved generalized benders decomposition method comprises the following steps: the method adopts a generalized Becders decomposition method to decompose the time delay function of the vehicle user into a main problem and a sub problem, and comprises the following steps:
step 1: according to the generalized Becders decomposition method, a sub-problem is obtained by fixing the unloading decision and the caching decision binary vector in the time delay function of the vehicle user; and the subproblems have optimal solutions;
step 2: if the subproblem can be solved, the subproblem has a unique continuous solution, and the corresponding Lagrange multiplier lambda is obtained, and the optimal objective function value of the subproblem is the effective upper bound of the time delay function of the vehicle user; obtaining a feasible cut of the sub-problem according to the continuous solution, and adding the feasible cut into the main problem as a constraint condition;
if the subproblem does not have a feasible solution, zooming the subproblem to obtain the subproblem with the feasible solution; solving the subproblems with feasible solutions by using a Lagrange method, simultaneously solving the infeasible segmentations of the subproblems by using an external approximation method, and adding the infeasible segmentations into the main problem as constraint conditions;
and step 3: solving a main problem min of a time delay function of a vehicle user according to constraint conditions of feasible cutting and infeasible cuttingeG; performing finite iteration on the main problem according to constraint conditions of feasible cutting and infeasible cutting and constraint conditions of integer cutting to obtain an optimal objective function value of the main problem, wherein the function value is an effective lower bound of a delay function of a vehicle user;
and 4, step 4: checking each unloading decision and caching decision according to a time delay function of a vehicle user;
and 5: the unloading task is converted into a vehicle local calculation task, so that the total time delay of a vehicle user is reduced;
step 6: stopping the check when the total time delay of the vehicle user reaches the minimum value; and simultaneously outputting the unloading decision, the caching decision and the resource allocation strategy at the moment, wherein the strategies are the optimal resource allocation scheme.
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